app_id in echo message

[Khodl]

Notice: Undefined index: app_id /vendor/kerox/messenger/src/Model/Callback/MessageEcho.php on line 86

It happen when the app subscribed to echo messages, and the user click on "Send Message" on a page's post. Facebook then sends the post as a message, and that's probably why the app_id doesn't exist.

Here is an example of data:

{"object":"page","entry":[{"id":"123456789","time":987654321,"messaging":[{"sender":{"id":"123456789987654321"},"recipient":{"id":"987654321123456789"},"timestamp":1503948277841,"message":{"is_echo":true,"mid":"mid.$XXXXXXXXX","seq":100000,"attachments":[{"title":"Here is an example","url":null,"type":"template","payload":null}]}}]}]}